The mixed-lineage leukemia (MLL) protein is a histone methyltransferase critical for the epigenetic regulation of gene transcription. Many acute leukemias, including acute myeloblastic leukemia (AML), acute lymphoblastic leukemia (ALL) and mixed-lineage leukemia (MLL), are characterized by the presence of chimeric MLL fusion proteins that result from chromosomal translocations of the MLL gene located at chromosome 11, band q23 (11q23). Chimeric MLL fusion proteins retain approximately 1,400 amino acids of the N-terminus of MLL, but are fused with one of approximately 80 partner proteins (e.g., AF4, AF9, ENL, AF10, ELL, AF6, AF1p, GAS7). MLL fusion proteins lack the original histone methyltransferase activity of the C-terminus of MLL and gain the ability to regulate transcription of numerous oncogenes, including HOX and MEIS1, resulting in increased cell proliferation and decreased cell differentiation, ultimately leading to leukemogenesis.
The menin protein, which is encoded by the Multiple Endocrine Neoplasia (MEN) gene, is a ubiquitously expressed nuclear protein that engages in interactions with DNA processing and repair proteins, chromatin modifying proteins and numerous transcription factors (Agarwal, et al.; Horm Metab Res, 2005, 37(6): 369-374). The association of menin with the N-terminus of MLL fusion proteins is necessary for the observed oncogenic activity of MLL fusion proteins. This association has been shown to constitutively up-regulate the expression of HOX and MEIS1 oncogenes and impairs proliferation and differentiation of hematopoietic cells leading to leukemia development. Since menin has been shown to function as a general oncogenic cofactor in MLL-related leukemias, the interaction between menin and MLL fusion proteins and MLL represents a potential chemotherapeutic target.
Patients, especially infants, with leukemias harboring chromosomal translocations of the MLL gene have a dismal prognosis, with less than a 40% five year survival rate (Slany; Haematologica, 2009, 94(7): 984-993). A novel therapeutic strategy is urgently needed to treat these leukemias. Small molecule inhibitors that block the menin-MLL interaction are thus valuable targets for treating diseases involving the MLL fusion proteins.